The inventors have found that the thermal functionalization, especially maleation reaction, of vinyl terminated propylene-based homopolymer (and copolymer of propylene with higher alpha olefins such as 1-butene and 1-hexene) exhibits slower kinetics than that of vinylidene-terminated polyisobutylene of comparable number average molecular weights (Mn) in the range of about 500 to 3000 g/mol. For example, commercial highly reactive PIB (Mn 750 g/mol, vinylidene terminated, about 83-87%) undergoes maleation in the presence of 1.6 equivalent of maleic anhydride (MA) at 190° C. under about 1 atmospheric pressure (glassware conditions) for about 2 hours to afford a PIB-SA material with about 1.11 succinic anhydride functionality per polymer chain (e.g., see Example 1 below). In comparison, vinyl-terminated atactic polypropylene (aPP) of Mn about 1000 g/mol only gave a PP-SA material with less than 0.21 succinic anhydride functionality per polymer after 2 hours at 200° C. at about 120-140 psi of nitrogen when 2 equivalents of MA was used in autoclave (see, for example, Example 6 below). Consequently, long reaction times (between 30 to 80 hours) and/or large excess maleic anhydride are typically needed for achieving high conversion of the vinyl at temperature of 190° C. or below.
It is not understood why the rate of maleation of vinyl-terminated PP is so inefficient and it is unexpected that it should be slow. The lower reactivity of the vinyl double bond versus the vinylidene double bond may be rationalized in terms of the relative reactivity steric hindrance of the allylic hydrogens when the six-membered-like cyclic transition state is adopted by the two reactants (three methyl hydrogens in vinylidene versus two internal methylene hydrogens in vinyl). A technological need therefore exists for identifying a practical method with conditions that would provide high degree of functionalization of vinyl double bond with anhydride group toward thermal “ene” reaction (with maleic anhydride or other olefinically unsaturated carboxylic acid derivatives).
Related disclosures include U.S. Ser. No. 13/804,727 filed Mar. 14, 2013; U.S. Ser. No. 13/804,507 filed Mar. 14, 2013; US 2010-0170829; US 2009-0318646; U.S. Pat. No. 7,183,359; R. Mülhaupt et al. “Novel Polypropylene Materials Derived from Vinylidene-terminated Oligopropenes” in 4 POLYMER FOR ADVANCED TECHNOLOGY pp. 439-449 (1993); R. Mülhaupt et al. “Reactive Blending of Polypropylene/Polyamide-6 in the Presence of Tailor made Succinic Anhydride-terminated Oligopropene Compatabilizers” in 4 POLYMER FOR ADVANCED TECHNOLOGY pp. 465-474 (1993); A. S. Sainath “Synthesis and Characteristics of Succinic Anhydride- and Disodium Succinate-Terminated Low Molecular Weight Polyethylenes”, 42(13) MACROMOLECULES 4356-4358 (2009); and M. Thompson et al. “Terminal Functionalization of Polypropylene via the Alder Ene Reaction”, in 39(2) POLYMER 327-334 (1998).